The main objective is to study the structure of viruses with nucleo-proteins and chromosomes. Particular emphasis on the internal organization of their nucleic acids. This will be attempted by using the remarkable optical properties of both DNA and RNA in their various chemical states (charge, single and double strandedness, percent of helical structure, etc.). The most important methods will be: a) Optical rotary dispersion (ORD) and circular dichroism (CD); b) Magnetic rotation (Faraday effect) and magnetic circular dichroism (MCD); c) Electric birefringence and dichroism; d) Flow birefringence and dichroism; e) fluorescence detected circular dichroism. These methods will give information concerning the following properties: a) The interaction between the bases of the nucleic acids, the nucleic acids and the protein complexes, and the protein coat with itself in the intact virus. b) The electrical properties of the protein coat and the average orientation of the nucleic acid in the virus. c) The hydrodynamic behavior of viruses in solution and the changes in such behavior under alteration of chemical environment. With the help of the above and other available information, it is hoped that models satisfying all the conditions can be made to give an insight on the organization of the whole virus or chromosome, and that through this research new diagnostic techniques of an optical nature can be developed for detecting and identifying viruses and studying the state of chromosomes in whole nuclei.